text:
Why is a downwind wind speed given in wind checks for aircraft on final?
I have a quick question about wind checks. When I spotting at Sydney (YSSY), I often hear tower clearing aircraft to land and giving them spot wind checks at the runway threshold, all pretty standard.
What I don't understand is when that wind check contains a downwind component.  For example:
QFA32, Wind 160/10 Downwind 2, Cleared to land RWY 16R

(That is an example and not a wind scenario I've heard.)
Am I overthinking this? Is the downwind component just given when they are landing with a tailwind?

I'm not sure that's part of the wind information, it sounds more like something about the number of aircraft landing. But I may be wrong, if no one knows then it would be great if you could find an example on liveatc.net or somewhere else.

Could you write exact wording you did hear/update with such wording when you hear it next time? Or find something in Live ATC (but I don't know whether it's available for Australia)? There might be some detail you are missing—and therefore failed to capture it in the example—that is important for interpretation.

Yeah, I'm guessing he's actually saying "QFA32, Wind 160@10, number 2, cleared to land runway 16R" rather than "downwind 2". Unless of course you can't clear number 2 to land in Australia, in which case, ignore me...

'Downwind' speed does indeed mean that the aircraft will be landing with a slight tailwind. Each aircraft/airline has a maximum downwind component which is acceptable to land with - generally about 5-10 knots. From my experiences as a private pilot in Australia, I have observed that ATC will tell the flight crew the current downwind component without being requested to do so. I find that they will also advise if the crosswind component is more than about 5-10 knots. It has been a few months since I last heard it but I believe the wording is along the lines of "Qantas 32 heavy, wind 210 at 7, maximum downwind 7 knots, runway 01 cleared to land". This information is also available on the ATIS.

Is this an Australian thing? I've never heard of ATC giving any more information than the usual wind direction/speed, and that tells the pilots anyway if there's a tailwind or crosswind. And in the OP's example there is no tailwind, but that might just be because he made up some numbers for the question.

I assumed it was used everywhere.. but I also thought every country used "line up behind the 737 on final", and apparently that is not the case! I am a private pilot based at an airport in Australia that also sees a fair bit of airline traffic, so my answer is based on what I hear over the radio. ATC have never cleared me for an approach with tailwind but it does happen for the airliners, and the ATIS also includes the downwind component, as well as the advice from the actual controller.

Very interesting! That doesn't happen in the US, at least, I have no idea about other countries. Well, I do now know about Australia :-) You might want to mention the ATIS in your answer as well, that's a useful piece of information.

@Pondlife 7110.65 3–5–3: When authorizing use of runways and a tailwind component exists, always state both wind direction and velocity. Nothing about explicitly telling the aircraft what the tailwind component actually is.


text:
Where do the names "First", "Business" and "Economy" class originate from?
As said in the title: where do the names "First", "Business" and "Economy" class originate from? Why they didn't use the names "First", "Second" and "Third". After all it can be hard for someone not that familiar with English to find out that "Business" is ranked higher than "Economy".

It's a mere guess so only a comment: "Second/Third" class do not sound too nice, do they? It sounds better when you link it to something positively connoted like: "business". It's not "first", but it still sounds appropriate for those people who think of themselves as important businesspeople. What's the image you have when hearing "business"? The same for economy: It does not sound good to fly "third class" (like third class, when people were still separated in social classes). But to travel in an "economic" way sounds good, doesn't it? It's mere PR gags, nought more.

I think what @PatricHartmann is trying to say is that they come from the Marketing Department. They still mean 2nd and 3rd class, they just sound nicer.

Yes, but what is known about the introduction. Why did they pick these names and why did all airline companies used the same ones.

why did all airline companies used the same ones.  They don't.  "Business" is often called "club". "Economy" is often called "coach".  American airlines often call "business", "first" on two class configurations and so on.

@PatricHartmann FWIW trains in the UK have "Standard" class rather than "Second" - a change which was made in the 80s for precisely the reason you suggest.

The current names are a progression.  A satisfying explanation of how passenger classes evolved from the era of trans-oceanic ships seems to answer your question...   https://en.wikipedia.org/wiki/Economy_class

@NigelHarper : That's an interesting insight, thank you; so is the Wiki article.

You might try asking this on English.SE as well

@Pondlife: I think double posting is against the rules on SE, but if you think the question is better migrated to the English SE, I have no objection.

It's no problem to repost on english.SE (but I would include a link back to this question). There's no option on aviation.SE to migrate to english.SE specifically so we've done this before.

@Pondlife [travel.se] might also be a good option, as they're more focused on passenger-related issues of travel.

@Simon Nonetheless, the only allowed class descriptions in an air fare is "FIRST" or "BUSINESS" or "ECONOMY" (alternatively "COACH/ECONOMY"). The wording of fare rules is constrained to the definitions published by the Air Tariff Publishing Company since nowadays all fare rules worldwide need to be understood by computers for autopricing purposes.

@Calchas Do you have a reference?  My understanding is that fares are based on letters only, e.g. "business" might be D, K or J.  Many US airlines call these classes "first", and I've had "FIRST" printed on a J class ticket.

@Simon The first letter denotes the prime booking code, or reservation booking designator. But every airline uses different groups of letters for different cabin classes (e.g., EI uses "F" for economy class, which can be confusing since almost everyone else reserves that for first class). The fare rules itself will state the class of service: see e.g. the following unrestricted "Club World" fare (J) on BA from Leeds to Miami http://pastebin.com/jsCP1u3w

@Simon but you are quite right, so if that international business class fare covers travel on AA within the USA, how do I decide which class I should book for reservations on AA? ["J", the prime code, will not be available on AA domestic flights without a business class.] To decide, we look at the Booking Code Overrides table for the fare: http://pastebin.com/E4zbuHRz You see that first I should book J if it's available—if it isn't, instead I should book F. Alas the system doesn't know which cabin that is, which is why some online agents get it wrong—we just have to keep a table up to date.

@Calchas Roger.  Thanks.

They used to use those ordinal class names (first, second, third), borrowed originally from train and ocean liner class designations. British railway classes were first, second and third classes, while ocean liners typically had first, second and steerage (which itself became a derogatory term that was changed to "third class", especially as steerage evolved from a converted section of cargo space to purpose-built passenger accomodations).
The change to the modern airline classes is an example of the euphemism cycle, and occurred through the 1960s and 1970s as travel in general increased dramatically while the average income of the travelers nose-dived. In the U.S., the primary driver was the stigma of people in those sections being called "second class" or "third class" as "political correctness" started becoming a big thing with the civil rights disputes. This led to a rebranding of lower numbered classes by airlines; second class, being a popular choice for frequent flyers on corporate business seeking a compromise between the low cost of the economy section and the amenities of first class, was renamed "business class", while the main passenger cabin holding the bulk of passengers with the lowest-cost tickets (average Joes going on vacation, visiting family or just needing to get somewhere on a short travel schedule) was called "coach", "economy" or simply "standard". All of these terms have survived at least informally, but "economy" is the one most often used by the airlines to denote this service level.

I'm not saying you're wrong about anything, but some references would be a great addition to this answer.

Here's a blog post talking about the dysphemistic nature of the term "third class" in the context of Britain's rail system and some plans to privatize and extend service options: http://blogs.spectator.co.uk/coffeehouse/2013/10/why-do-we-cringe-at-the-term-third-class/

That doesn't really strike me as much of a reference, but if you do find something, just edit your answer to include it.

@KeithS Interesting article perhaps but it doesn't really relate to the use of these class names in aviation.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

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Can you help me identifying this circa 1910 airplane with tail number 72?
Circa 1910 airplane with tail number seventy two
(Click for larger image)

It is a Wright, allright, but more probably an EX. The EX was a modified Model R, which in turn was a modification of the Model B. The R and the EX were single seaters, whereas the B would seat two.
Picture of a Model B replica, as taken from its Wikipedia article:

Picture of a Model EX, taken from this site.

The EX was the model used by Cal Rodgers for his epic transcontinental flight. Note the lengthened tail and the closer wings, which allowed to reduce rigging wire and, thus, drag. The "72" shows the same features, so I think it is a Wright Model EX.

Really appreciate all the help. I am so curious what the "72" is indicative of and what field it was in (empty grandstands in background) but I fear this may never be known. Thanks again guys :)

@VerticalLiquid: It is obvious from marks in the corners that the picture was in an album - do you still have the album? This might give more context.

Unfortunately I am an old photo collector and this was purchased by itself. I would love to have that album however ;)

@VerticalLiquid: It's good to know that collectors like you value those historic documents - if it weren't for you, the picture might not exist anymore. Not everyone takes so much care to preserve historic collections like Dean Putney, after all.

Thank you for the kind words Peter. It can be an expensive hobby but worth it. I find myself burning up the "whale oil" many nights going through my albums.

Looks very much like a Wright Model R. Some information can be found here, a picture from that site below:

(source: wright-brothers.org)

Looks very close, but the "72" has a bigger wing: Outside of the props, the Model R has only one pair of struts, but 72 has two.

@PeterKämpf indeed, you appear to be right.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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Could you help to identify this WW1 fighter?
Please help me identify this world war 1 fighter.

Pretty sure it's an Albatros C.I. Look at the access hatch with the double gills directly behind it, the three metal covers on the engine, the horizontal and vertical black marks on them, the upper wing support ending right between the two metal covers, the front support for the undercarriage ending right before the second gill.

Albatros C.I (Picture copied from the link above)
The Albatros C.III has a different tail, but that's invisible in the picture above.
Here is another picture, showing the plane from the other side. Note the flush radiator on the side of the fuselage. (image source)

The wing bracing looks wrong - notice how OP's wires go all the way to the center wing struts.

This is a great find! I think you are right.

Hope you don't mind that I embellish your answer - this is to strengthen your point.

@egid: I don't see the problem. The OP's picture crops the outer struts, as well as the rear inner strut. Still, all pictures show 3 wires going to the bottom of the front inner strut.

All three photo's seem to show different arrangements of cover etc. above the engine, but that is probably just "local mods"

First of all, this is not a fighter, but a C-type airplane. A C-type was a two-seater and was mostly used for reconnaissance or ground attack. That it is a German plane is obvious, but the picture leaves out the details like propeller, wings and fin shape which would help in identifying it.
Noticeable is the six cylinder in-line engine, the triangular fin and the boxy fuselage. Of particular interest is the position of the horizontal tail which starts well ahead of the vertical. This restricts the selection to these types:

Albatros C.III
AEG C.IV (but the tail details don't match well)
DFW C.V
Rumpler C.I
Rumpler C.IV to C.VII (they all looked very much alike)

From the limited information available, my best guess is the Rumpler C.I. See below for a side view from this source:

EDIT:
Now that MSalters has posted his answer, I think that he is right. It looks indeed like an Albatros C.I. I did not include this one in my search. Silly me.

The diagram doesn't include the hatch and two vents on the nose. Is that likely to be significant, or just missing detail on the diagram / a modification to the photographed plane?

The last source quoted has a picture which very clearly shows the tail section of a Rumpler C.I, and it doesn't have the offset between horizontal and vertical tail planes. Also, note the sharp upper edge of the boxy fuselage. It runs from the engine to the tail. On the Rumpler C.I this appears smoother.

http://www.wwiaviation.com/rumpler.html shows the C.IV having the frons access panel and the step behind the wing.

@DavidRicherby: You're right, but those details were not common to all planes of one type. Successful designs were built in several factories, and even with different engines, and each factory tried to add their own improvements. However, this might indicate that I am wrong.

@MSalters: … and the same link shows a horizontal starting well ahead of the vertical tail for the Rumpler C.I. I am not sure, the answer was just my best guess.


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Who decides whether an airline docks at a jetbridge or parks at a remote stand?
A trip I took led me to wonder how airports/airlines decide when to allocate a gate and when to board out on the apron.
Yesterday, I flew TLV-IST-BOS on Turkish Airlines. At the start of the trip, I briefly wondered if we were travelling to Istanbul (IST) by bus. The airplane was parked far from the gate.
We got to IST, and, once more to ride the bus. In this case, we parked at jetway, but we were sent down the stairs and onto a bus. Turkish sure is a big, legacy airline at IST.
And, to complete the process, our A340 for Boston was parked half-way to Europe, and reached by a bus.
What determines all this? Bad luck? Plane size?

It happened to me to in IST. The aircraft was most probably on maintenance and had just come out.

Its the money. Low cost airlines save by avoiding the more expensive jet bridges.

@CGCampbell, I actually think its more on topic here. It is about airline operations, not about travel advice. Though it should probably be reworded to something more generic along the lines "how are gates allocated to flights".

The current version is; when I made the comment above it was (IMO) not.

@PeterKämpf Sometimes it's that. Other times it's just because they don't have enough gates at a particular terminal. The international terminal at LAX is an example of this. I've deplaned off of a Cathay 777-300ER onto a bus there before. Before the new part of their international terminal opened, they only had 12 gates with jet bridges at their international terminal (despite LAX being #3 in the U.S. for international passengers, at 18.7 million/year.) They were parking A380s, 747s, and 777s at stands and bussing people in. Fortunately, they have a lot more gates with jetways now.

@reirab: Normally, in the US money decides who gets first access. I would be surprised if there was no bidding involved.

Why was someone nitpicking w/ that poor guy who used "tarmac" to mean "apron"?  That's a very common usage in the airport context.  I see the answer has been deleted now though.

This can depend on all kinds of things, so it's hard to give a definitive answer:

Many low-cost airlines park at remote stands as this is cheaper than parking at a jet-bridge.
Some airports have jet bridges that can't handle particular aircraft types (often large aircraft at small airports) and therefore these aircraft must park at remote stands.
Related to the above, some airports have no customs facilities for jet bridge arrivals (or vice-versa) and therefore international flights must be parked at a remote stand and passengers bussed to customs/immigration.
Sometimes a flight will be allocated a jet bridge in advance but then suffers from a delayed arrival. By the time it gets to the destination the jet bridge that was assigned to it is taken by another aircraft. In this case, the aircraft may have to be parked at a remote stand.
As you say, bad luck can play a role. Airports have a limited number of jet bridges and sometimes there's just no space for your aircraft.
Lastly, in my experience it is particularly common to get a remote stand if you arrive late in the evening: Some airlines like parking remotely in this circumstance as it's cheaper than parking overnight at a jet bridge.

As I said, it's hard to give a definitive answer but the above are some common causes for being placed at a remote stand.

The first point is also likely to affect regional flights even by legacy airlines.


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What are the ACARS frequencies and what is their usage?
I have been playing with a SDR dongle. I have been able to decode some ACARS signals using SDR# and acarsd. I have noticed in my area (35 miles west of DFW airport) there are a number of frequencies used. I have been able to decode transmissions on 130.450, 131.125, and 131.475. Are there other common frequencies? What determines the frequency used by a particular plane? I find it odd that I can pick up an AA flight 30 miles away and yet when a similar flight passes directly overhead, I am unable to find their ACARS on any of those frequencies.

According to the specs ACARS supports direct to satellite linking so planes flying over you may not be broadcasting on one of those frequencies. Similarly, if broadcasting over VHF you are line of sight limited. At high altitudes you may see ranges up to 200 Nautical Miles however if the planes are low overhead they may not be broadcasting as they are out of sight of the possible ground station. Your dongle may also filter/ignore low power signals or it simply cant pick up certain signals due to their strength.
Here is a list of common ACARS Frequencies.


text:
What is the meaning of ACAI and ATCI in Air Cadets?
For my staff cadet course, I need to know what ACAI and ACTI stand for but I can't find it anywhere. Would anybody be able to notify me of what this means?

The only ACAI abbreviation related to aviation I know is for the Afghanistan Civil Aviation Institute, but somehow I doubt that's what you're looking for.
EDIT: After some research I've found another one: Aerostar Continued Airworthiness Instructions. For hot air balloons manufactured by Aerostar.

I've also noticed that in the question heading it says "ATCI" but in the question body it says "ACTI".

I can't answer your question, but if you're already in the Air Cadets then you hopefully have a better chance of finding an 'official' answer than the rest of us. So if and when you do, please feel free to answer your own question, that's absolutely OK here.

Those four letters can be abbreviations for many things related to aviation. Taking into account that this is for a staff cadet course, I think the most likely candidates are:

Air Cadet Administrative
Instructions
Air Cadet Training Instructions

Source

ACAI could stand for following:

Afghanistan Civil Aviation Institute.
Some building in Serbia, which is related to aviation. (Source)
Air Cadet Administrative Instructions. (Source)

ATCI stands for Air Traffic Control Instruction.
This acronym appears very rarely. And refers to training of Air Traffic controllers.


text:
Can I fly solo when practicing IFR under the hood?
If I have my instrument rating can I log simulated instrument time under the hood while flying alone as the PIC? Or does a safety pilot have to be present?

If you're flying under the hood in VFR, how do you watch out for traffic?

I think he means flying on an IFR flight plan in VMC while simulating IMC "under the hood"

In VMC, even pilots operating IFR are required to "see and avoid" VFR traffic.

Before going into the FAR AIM, take a second to think about this idea:
You are in your airplane, under the hood, flying along your route or wherever. The only traffic warnings you will get are from your controller, and he does not always see all the VFR traffic on his screen... Not a good idea. Definitely never fly without a safety pilot under the hood in VMC.
Now lets open the FAR AIM:

§91.109 Flight instruction; Simulated instrument flight and certain
  flight tests
(c) No person my operate a civil aircraft in simulated instrument
  flight unless -
(1) The other control seat is occupied by a safety
  pilot who possesses at least a private pilot certificate with category
  and class ratings appropriate to the aircraft being flown.
(2) The safety pilot has adequate vision forward and to each side of
  the aircraft, or a competent observer in the aircraft adequately
  supplements the vision of the safety pilot; and
(3) Except in the case of lighter-than-air aircraft, that aircraft is
  equipped with fully functioning dual controls. However, simulated
  instrument flight may be conducted in a single-engine airplane,
  equipped with a single, functioning, throwover control wheel, in place
  of fixed, dual controls of the elevator and ailerons, when—
(i) The safety pilot has determined that the flight can be conducted
  safely; and
(ii) The person manipulating the controls has at least a private pilot
  certificate with appropriate category and class ratings.

Getting the important stuff out of there: No person may operate a civil aircraft in simulated instrument flight unless the other control seat is occupied by a safety pilot!
The FAR/AIM part obviously only goes for FAA regions, but I'm assuming that is what you are asking about.
Conclusion: According to logic thinking you should never ever not look out the window in VMC, and the FAA doesn't allow you to either, not even for IFR recency!


text:
When crossing a mountain ridge at low height above terrain what consideration is given to turbulence?
Some background: I am not a pilot, but a researcher studying air-flow across mountain terrain using Computational Fluid Dynamics (CFD).
During my studies, I have been particularly interested by high-altitude ridges (2 to 3000m a.s.l., say 10000 ft) that are exposed to regional winds that are generally across the ridge. I have been seeing very interesting turbulence patterns above, and in the lee of the ridges (rotors).
Here is the question: what instructions are given to pilots needing to cross such a ridge at low heights above the terrain, in either direction relative to the wind? What does common sense dictate?
I am naturally thinking mostly of helicopter pilots doing mountain work, but any other aircraft are very welcome (fire-fighters, ULMs ...).

What instructions? - "Remember Steve Fosset"?

@RedGrittyBrick Yep, I can imagine that is not the desired outcome of a flight. :-) Basically, I am looking for anything ranging from instructions given by official bodies, down to the more direct language a flying instructor could use inside the cabin. Anything more precise than just "stay the h*** away from it!" The reasoning behind such instructions would be most interesting.

I've done a little helicopter mountain flying, as number 2, and the general rule is "don't fly on the leeside".  If you need to cross a ridge, and the wind is behind you, don't cross the ridge.  There is a theoretical line called the "demarcation line" where the wind changes from rising, on the windward side, to falling on the leeward side.   The falling air, coupled with the possibility of rotors as you mention, combine to "don't fly there".  Don't cross the  ridge, fly along it and look for an alternative - plan ahead!

I found this which might be useful

@Simon, thanks for the link, there is a clear figure that shows the demarcation line you mention.

We often find lift on the leeward side is the ridge. It's more complicated than those diagrams show

@rbp "We" = glider pilots, perhaps? I suspected as much. Will be consulting the reference you gave below with interest.

@RedGrittyBrick : Thanks for that Steve Fosset link, it kept me busy for hours. I did not know that he died in an aircrash. The story is nothing short of a movie plot. I even searched wikipedia, came to know about Brietling watches that have inbuilt ELT, the way his body was found, how animals had dragged his remains etc. RIP Steve.

From an older FAA Publication on mountain flying:

Mountain Wave
When the wind speed is above about 25 knots and flowing perpendicular to the ridge lines, the air flow can form waves, much like water flowing over rocks in a stream bed. The waves form down wind from the ridge line and will be composed of very strong up and down drafts, plus dangerous rotor action under the crests of the waves. If enough moisture is present, lenticular clouds can form to give a visual indication of the wave action. These clouds are reported in the remarks section of hourly sequence reports as ACSL (altocumulus standing lenticular) or CCSL (cirrocumulus standing lenticular)

Pretty much sums up what you're seeing I guess. As for action:

Ridge and Pass Crossing
On most mountain flights, you will need to cross at least one ridge or pass. Experienced pilots recommend crossing a ridge or pass at the ridge elevation plus at least 1,000 feet. If the winds at mountain top level are above 20 knots, increase that to 2,000 feet. Plan to be at that altitude at least three miles before reaching the ridge and stay at that altitude until at least three miles past it. This clearance zone will give you a reasonable safety zone to avoid the most severe turbulence and down drafts in windy conditions.
If conditions or airplane performance dictate, you may need to fly along the windward side of a ridge to find updrafts for gaining altitude before crossing a ridge. You may also need to circle before reaching the ridge if climbing out of a valley airport. When you actually cross a ridge, you should do so at a 45• angle to the ridge. This allows you to turn away from the ridge quicker if you encounter a severe downdraft or turbulence. Once you have crossed the ridge, turn directly away from it at a go• angle to get away from the most likely area of turbulence quickly. Plan your crossing to give yourself the ability to turn toward lower terrain
quickly if necessary.

As for helicopter mountain flying specifically, I'm afraid you are unlikely to find somebody on here with that experience. You might have better chance on searching for it online and phoning up flight schools that offer such courses (I found a few in the states) for information.

This is the type of instructions I was looking for, thank you. "you should do so at a 45• angle to the ridge. This allows you to turn away from the ridge quicker" The rationale behind this is not clear to me: would going straight across not be a better way of getting out the downdrafts encountered?

@ALANWARD If you're flying towards a ridge and you encounter very strong downdrafts, then you may not be able to get over the ridge at all. That means you need to turn back and being at a 45° angle means you can turn away with a 90° turn or even less. If you were flying straight at the ridge you would have to make at least a 135° turn (or whatever) to do it, requiring more space to turn. Mountain flying can mean limited room for maneuvering (including vertically; a light aircraft could be close to its service ceiling), so always having a way out is really important.

@Pondlife OK, so that would be flying towards the ridge from the leeward side. Understood, nice comment.

@ALANWARD: It is easier to always approach ridges at angle than think about whether you are approaching from leeward side and need it or windward side and don't. So it's needed when you are approaching from leeward side, but it's recommended always to keep the procedure simple.

@JanHudec Makes perfect sense, to keep it simple.

Power pilots (which I am also) are the wrong pilots to ask about this topic. We are trained to stay away from this kind of topography for all the reasons listed
Glider pilots fly ridges and mountain wave all the time, very close to the ridge line. Ridges and mountains provide all sorts of lift, which is the key to great soaring, and we are taught to fly IN it, not away from it.
My recommendation is to read the first part of Helmut Reichmann's Cross-country Soaring called "Flight in Lift" which details the answers to the questions you're asking.
As far as helis are concerned, which I also fly, the the big considerations for mountain flying is how much excess power you have. When you encounter a downdraft in a heli, you  have to add power to arrest a decent, so it's important to know your power, weight, and density altitude limits. There are a few helis that are known as good mountain machines, like the AS350.
In any aircraft, if you're going to fly in the mountains, you have to be able to read the signs: surface winds and winds aloft, cloud patterns, areas of airmass convergence, etc

I was wondering what glider pilots are told, thanks for the reference.

Interestingly, AS350 around where I live are used mostly for sanitary transport between hospitals (small regional to large), just flying down large valleys. But they also get to do some primary intervention from time to time, which makes for more "interesting" flying.

I regularly watch a couple of YouTube pilot video channels and this particular one had a recent series on mountain flying.  There too much there to re-state here but I think this particular video would be very interesting to you.

There are additional videos from this series that you might also find helpful.

Yeah, the instructions are DON'T GO NEAR ROTORS OR YOU MIGHT DIE.
You never want to pass close over a ridge, even if does not have lenticular cloud or other visible sign of downdraft. Once you get caught in the down draft it can be almost mathematically impossible to escape. My instructor's instructor was killed in Maine by trying to cross a mountain too close.
The procedure is to navigate to a valley or pass where you can clear the mountain by a healthy margin.

You seem to confirm the impression I had - that most pilots consider low-level mountain flying a bit like a death trap. I wonder what a "healthy margin" could be - and how to figure it out.

Eh, you might die from lots of stuff. Every glider pilot who has flown wave has encountered rotor. Rarely kills 'em. Oh and You're thinking of the down wave, not the rotor, which, as the name implies rotates, not just down drafts.


text:
Can water landing be simulated?
Is is possible for a flight simulator software to simulate the real time scenario of landing an aircraft on a water body. There are instances of this (Ethiopian Airlines Flight 961, US Airways Flight 1549) and the results were catastrophic/great  based on the type of water body they landed on and the situation which brought them there and several other parameters.
But I want to know if it is possible for a complex computer program to create this scenario effectively and thereby better equip the pilot ?

I like "water landing" as an euphemism for "an airplane crash in the water."

Technically yes, but I do not know of any simulator which includes this. The water forces can be calculated in the same way as the air forces, so I see no reason why it should't be possible.
Historically, model tests were made to check that a new airplane would behave well when landing on water. The simplest tests would use a catapult and launch the aircraft model into a lake, and more thorough tests use water tanks where the airplane model is pulled along the water surface while being suspended on a rig. This allows to measure forces, while the catapult launch will only show the dynamics of a water landing. Results like these could be used to calibrate the computer model, so you can be sure it behaves like the real thing.

afaik, the problem with the simulation of such an impact is the free surface condition (the boundary between air and water): it creates several complications in simulating the behaviour of the water mass and thus in computing the forces exerted.

@Federico: Yes, this is a complication. Either you use adaptive nets and get a very detailed, but slow, calculation, or (for driving a simulation) do it with approximations which will cover most cases well enough.


text:
Minix wingtip vortices mitigation - How does it work?
I stumbled upon this article: Minix wing tip device promises 6% gain in fuel efficiency for airliners.

Such an economy is appealing and I must confess the design is "sexy".
Could someone expand a little bit?

those grooves should be twisted the other way to minimize the vortex, as is it seems like it would aid in vortex creation

The tiny mass of air that this device can affect will in no way have the claimed effect on induced drag. This wingtip vortex pseudoscience is just bullshit. What can be observed as a vortex behind the wing is actually the consequence of the vortex sheet rolling up due to downwash behind a lift-generating wing. But air flowing around the tip has almost nothing to do with it.
I would compare it to those magnetic rings you are supposed to put around your fuel line to save fuel. Snake oil, in other words. There is no way this thing can reduce the wing's vortex, all it will do is to create some more local turbulence.
All it needs is a slick salesperson, a few gullible people with too much money and greed, a big promise, and the scam takes its course. This can easily yield enough investment money to allow all scammers to drive a Ferrari for a year or more. Now they have a year to come up with the next big thing.

Does all that apply also to regular winglet?

Maybe VX Aerospace can tell if they came to agreement?

@menjaraz The main advantage of wingtip devices is in preventing the vortex from "spilling over" onto the top of the wing - there's a lot of reasons they can help, but like Peter noted the size (and honestly the core concept) of this device makes me think it's unlikely to have any significant measurable effect. See also this video.


text:
Can I bring a person with me while getting landing current if they're a licensed, current pilot?
It's been over 90 days since I've been flying, but I have a biennial flight review coming up pretty soon and would like to prep for it.
The regulations regarding this seem to be extremely vague, but is it legal for me to fly around, do my landings, log PIC time, and such with another licensed, current pilot in the plane with me?

As long as  you are not the legal pilot in command you can do what you want.  This means the other pilot has to be willing to act as the legal pilot in command on this flight.

61.57(a) General experience.
(1) Except as provided in paragraph (e) of this section, no person may
  act as a pilot in command of an aircraft carrying passengers or of an
  aircraft certificated for more than one pilot flight crewmember unless
  that person has made at least three takeoffs and three landings within
  the preceding 90 days, and—
(i) The person acted as the sole manipulator of the flight controls;

The regulation is clearly required of the legal pilot in command.  If your current passenger is willing to act and take responsibility for your flying as the legal pilot in command then it is allowable.
Unfortunately, the other pilot is taking all the responsibility and gets none of the credit as they, under an airplane certificated for single pilot operations, cannot log any PIC time while you are getting current.
From LOGGING PILOT IN COMMAND TIME (FAA):

However, two pilots may not simultaneously log PIC when one pilot is
  sole manipulator of the controls and the other is acting as
  pilot-in-command if the regulations governing the flight do not
  require more than one pilot.

If the other pilot is a CFI and it is a training flight then no one has to be landing current as there are no passengers.  See the Kortokrax interpretation.
Relevant excerpt:

We agree that, for purposes of section 61.57(b), an authorized
  instructor providing instruction in an aircraft is not considered a
  passenger with respect to the person receiving instruction, even where
  the person receiving the instruction is acting as PIC. (The instructor
  must be current, qualified to instruct, and hold a category, class and
  type rating in the aircraft, if a class and type rating is required.)
  The instructor is not a passenger because he is present specifically
  to train the person receiving instruction. Neither is the person
  receiving instruction a passenger with respect to the instructor. This
  training may take place, even though neither pilot has met the
  61.57(b) requirements.

I'm not sure that this is true. It might be worth getting a FSDO interpretation, but it goes against everything I've understood about acting/logging PIC.

@egid Remember that to the FAA, acting as PIC and logging PIC are completely different things.

@egid What do you disagree with?  This is actually pretty clear.

I do not agree with this answer. The regs clearly say no one else, and no property either, during the flights where the pilot wants to regain currency.

@JuanJimenez The regulations say that the pilot in command must be current if there are any passengers. Under the proposed scenario, the pilot in command is current. So, that means it's okay.

@TannerSwett That is not correct. The desired result is for a pilot who cannot act as PIC to regain currency. For that to happen the pilot who wants to achieve that must be the PIC and may not be in the airplane with anyone else, or with any property. It's crystal clear, not legal to claim currency if there is another pilot in the plane with you.

@JuanJimenez I don't think that's correct, and I have another question for you, but the comments on this answer aren't the place to talk about this. Can you please create an answer post explaining your point?

The answer to why your point is incorrect is spelled out in 61.57(2). It's posted verbatim in the first answer below. To achieve currency, there can be no persons or property in the aircraft other than the pilot who wants to achieve currency. This doesn't need any further explanation.

@JuanJimenez.  You are confusing logging PIC time with acting as pilot in command.  You don’t have to be the legal pilot in command to regain landing currency.

@wbeard52 You are reaching for something that is not there. If the FAR unequivocably states that there can be no other persons on the aircraft, the pilot has to be the PIC. If you can find some magic way that someone can be flying solo and not be PIC, let us know.

@JuanJimenez 61.57(a)(2) “a person may act as a pilot in command of an aircraft under day VFR or day IFR, provided no persons or property are carried on board the aircraft.  If the person getting landing current is the legal pilot in command then no other people can be on board.  If another is the legal pilot in command than they can be on board.  Notice the word may instead of must.  Regs are very clear in this matter.

@wbeard52 If the the other person is the legal pilot, you cannot claim you have become current. You cannot selectively take things out of the regs to make a point. "For the purpose of meeting the requirements of paragraph (a)(1) of this section..." I'm done arguing this with you. You think you're right? Try it and see what the FAA thinks about that. Or better yet, try it, have that pilot get into an accident and see what the insurance thinks about your interpretation. Good luck with that.

@JuanJimenez.  Did you not read the legal interpretation listed in the answer.  That is the FAA saying what I’m arguing.  No reason to be rude, we are all here to learn.  There are holes in your understanding though.  Feel free to ask the FAA for an interpretation affirming this answer.

@wbeard52 Have you read it yourself? It only references 61.57(b), which has nothing to do with the landings currency referenced in 61.57(a), the subject of this question. My understanding of this is watertight. I suggest you read it again, carefully this time.

I don't think it's that ambiguous. The kicker in your requirementsis the "log PIC time" part...
CFR 61.57

(a) General experience.
(1) Except as provided in paragraph (e) of this section, no person may act as a pilot in command of an aircraft carrying passengers or of an aircraft certificated for more than one pilot flight crewmember unless that person has made at least three takeoffs and three landings within the preceding 90 days, and—
(i) The person acted as the sole manipulator of the flight controls;

And this section:

(2) For the purpose of meeting the requirements of paragraph (a)(1) of this section, a person may act as a pilot in command of an aircraft under day VFR or day IFR, provided no persons or property are carried on board the aircraft, other than those necessary for the conduct of the flight.

So I interpret that as no passengers. If the other pilot is a CFI and giving instruction, then that would count but if they are just going for a ride, no its not "legal". The take offs and landings have to be done either solo, not as PIC, or under instruction.
The other person may be a pilot, but unless they are performing pilot duties they are a passenger like any non pilot rated passenger. By the way,  the PIC does not have to sit on the left, you can still occupy the left seat as long as your pilot friend accepts PIC responsibilities as you complete your currency then you can resume being PIC.

Not sure if I agree with this interpretation. The way I conclude, from your highlighted statements, is (1) the person trying to get current has to be the sole manipulator of the controls, AND (2) the other pilot (who is current) acting as PIC.

Don't you need to be certified in some way to fly from the right hand seat? If I'm correct that means the average pilot cannot act as PIC from the right (unless there is some odd loophole that says the PIC doesn't have to actually be able to fly the thing).

@Ben -- that's worthy of asking a new question

@kevin that is correct. The PIC doesn't have to be the one manipulating the controls. See http://www.aopa.org/Pilot-Resources/Learn-to-Fly/Aviation-Subject-Report-Logging-Pilot-in-Command-PIC-Time

@Ben No,  there is no regulation that says you need special training to fly right seat. You can sit wherever you like as long as you can safely manipulate the controls.

It's fine to fly from the right seat. But some older bonanzas have a "throw over" control yoke, which I wouldn't act PIC from the right seat in unless I also had the yoke

FWIW, I believe that wbeard52's answer is correct: 61.57 says the acting PIC must be current to carry passengers; it doesn't say that the person at the controls must be current.
If you consider AOPA to be an authoritative source, their February 2011 Legal Briefing column discussed exactly this question:

Q: I’m out of currency to take passengers in my Cessna 172. When I go
  flying to do my three bounces, I would prefer to have someone with me
  for an extra set of eyes and ears. Does it have to be a CFI or can it
  be a private pilot, as long as he or she is current?
A: [...] if the private pilot is current and is willing and qualified
  to act as PIC of the aircraft, that pilot may be on board the aircraft
  as PIC and you could be the sole manipulator of the controls in
  getting your three bounces. I would make sure that both of you
  understand your roles in the aircraft before taking off, to avoid any
  misunderstandings.

authors: Тетяна Олегівна Аліфіренко


text:
In a constant speed propeller, why does the RPM drop with a prop pitch increase?
When a constant speed propeller changes its pitch from low to high, RPM would decrease.
Why is that the case?
Wouldn't the RPM increase when we increase the blade angle since there's less drag and the blades are more aligned to the relative wind, compared to when it's in a low pitch angle? Also, does higher blade pitch allow us to fly any faster?

You're right, it's correct now.

Yes, but why is that the case is what I'm trying to figure out.

I was thinking alongside of the same thing, since AoA would be higher like you said, but if the prop was feathered, it would minimize drag compared to a windmilling prop since the feathered prop is more aligned to the relative wind compared to a windmilling prop, correct?

The propeller blades indeed have least resistance when aligned with the inflowing airstream, however the inflowing airstream is not the free stream at infinity, but the vector sum of free stream velocity $V$ and rotational velocity of the propeller blade $\omega \cdot r$.

In the picture the local Angle of Attack is indicated as $\alpha$. Increasing blade pitch results in increasing $\alpha$, which means more air accelerated backwards: more thrust delivered, and more torque required.

Koyovis explained it with maths and cool diagrams, here is my layman's version, if it helps.
You're confusing aircraft drag with the drag on the prop. Since the prop is powered, it typically produces thrust not drag with respect to the aircraft. It only produces a net drag if it's windmilling (that is being turned more by the airflow than by the engine) - which is why you would feather the prop on a dead engine in a multi-engine aircraft.
Each prop-blade however produces drag in the direction they're travelling (i.e. sideways) in order to produce lift in the direction the aircraft is moving (i.e. thrust) - and it's this drag the engine is fighting. Increasing the pitch makes it harder to swat that thing through the air (but also produces more thrust) thus the engine RPM goes down.

Best answer.  For basic questions such as this the layman's explanation is generally always preferred...


text:
Why is Denver International Airport runway 16R/34L rarely used?
From watching planes land at DIA on Flightradar24, none seem to ever land on 16R (longest runway in the US at a length of 16,000 ft), but instead land on a runway 4,000 ft shorter such as runway 16L (12,000ft). So why do even large planes like the 747 not land on the longer runway to have an easier landing?

@fooot No, but I used to look at flightradar everyday for about 2 months and never saw any airplane land on the runway. I edited the question, instead of saying never I said rarely.

You could mention that you watch but never see airplanes land there, and maybe the 747 as a case where you most expected it.

@fooot I have seen a few 747's land on radar and none landed on the runway. Its not just 747's it can be 767's or 777's that I have seen on radar land at the airport, but never used the long runway.

I edited the question to make the wording more about why planes don't land on that runway in general, rather than why one specifically didn't.

Since a 7x7 can land on the 12,000' runway 16L, there's no need for it to land on the 16,000' 16R, therefore, there's no need to push traffic to the west and make it have a longer taxi into the terminal. I'm sure when things get really busy, they use 16L/34R.

They are landing 16R right now...

Wait for a day when it's 100F+ in Denver and then go look.  I'm sure you'll see heavier usage then.

KDEN has a lot of runways, so they have the option of not always using some of them. As FreeMan pointed out, 12,000 feet is plenty for just about any aircraft flying in or out, even at 5,300 feet elevation. Being such a long runway, it may also be good to leave it open so that no aircraft need to be moved in case an aircraft declaring emergency would need the extra length. Runway use will depend on the wind and traffic, so depending on when you are observing, you may not often see conditions where it is used.
North flow: arrivals on 34L could interfere with runway 7/25, and for departures it is further from the terminal than 34R. TomMcW also points out potential noise abatement concerns.
South flow: departures on 16R could interfere with runway 7/25, and for arrivals it is further from the terminal than 16L.
Even with 17L/35R currently closed it is not always necessary to use 16R/34L. 8/26 and 7/25 can be used for east/west departures and arrivals, and 17R/35L can be used as well.
Runway 16R/34L can still be used as a secondary runway though. It can certainly be used as 16R for parallel approaches with 16L, or departures as 34L with approaches on 34R.
To put things in perspective, Denver has more runways than both KLAX and KATL, which see more aircraft movements.
Also, while far from authoritative, the virtual Denver ARTCC lists 16R/34L as a secondary runway in all situations.

Doesn't help the OP, but this planning document suggests that 16R/34L is a primary use runway in all situations.  http://www.faa.gov/airports/planning_capacity/profiles/media/DEN-Airport-Capacity-Profile-2014.pdf

@BowlOfRed Thanks for the info. The document lists all runways, but 16R/34L is down on the list, and it does say: In 2003 DEN commissioned a new runway, 16R/34L, which typically experiences mixed use.

Twelve thousand feet is a really long runway; during clear & dry conditions the extra four thousand feet of 16R isn't any added value.
Where the extra length becomes really valuable is takeoff during winter ops when the runways have enough snow on them that braking action (i.e. in the event of an aborted takeoff) is degraded, and the anti-ice systems on the aircraft are all running (reduces engine performance), and you have some really heavy aircraft.  At that point, given the high altitude at KDEN, then the extremely long runway DOES become more advantageous than the others -- especially for those heavy weight & performance limited aircraft.
But for landings on good weather days when the airport has 6 strips of concrete (actually 5 at the moment, as 17L/35R is closed for repairs for some length of time) to choose from, you simply don't need them all.  Departing on 16R probably won't happen, because it's such a long taxi from the terminals, but departing on 34L seems fairly common... depending on where you're starting from, it's no more of a taxi than runway 8 or 25.  I've also landed (fairly recently, in fact) on 16R during good weather summer ops: arrivals from the west were getting 16R and arrivals from the east were getting 16L.  Departures were using 17R (not an ideal runway for arrivals anyway, given the taxi back north to the terminals), and the east/west runways were either being inspected or temporarily shut down so they could reverse the flow (i.e. switching from landing 26 to departing on 8, and/or landing on 7 to departing 25, or vice versa).
And I've landed on 16L enough times with traffic for the parallel 16R close by, that I don't think I agree with the premise of the question.

I would assume it's also valuable in the hot summer months, given Denver's altitude. A heavy taking off to, say, Asia at 100F from a runway that sits above 5,300' is going to need quite a bit of runway.

@reirab Exactly.  I vaguely remember a press release when they built that runway which stated the reason was to allow a fully loaded B777 departure in the summer to support a non-stop to Japan.

What time are you usually watching radar?
Just a guess, but the following paragraph from this document would suggest noise abatement procedures.

Runways 34L and 34R :  Aircraft will be assigned headings of  355 to 010 degrees.   Intersection departures on  Runway 34L permitted if  user has  signed an agreement with the City and County of  Denver regarding terms of use .  The City may request that FAA stop allowing  intersection  departures if  the City determines that use of the procedure is resulting in detrimental noise impacts

This map shows you might not want to buy a house off the north end of the runway!

Note that the airport owns much more land than it uses operationally so it's not possible to buy a house particularly close to the runway ends, unless the airport sells you the land. The airport owns 53 square miles but all the runways fit into a rectangle of about 25 square miles and an irregular shape of about 12 square miles.

Let's just hope the airport never sells off the extra land and allows residential development. You know the first thing the new residents will do is complain about the noise - that's been there for 10,15, 20 years before they chose to move in!   /rant...

This is one possibility. However I was listening yesterday and they were south flow, and seemed to be using 16L but not 16R, so this isn't the whole picture.

16R/34L is normally used for departures only. Having a long runway for departures ensures that even the largest aircraft can depart fully loaded. I do see a couple of configurations utilizing that runway for arrivals, but it's always in VMC conditions when the airport is in a south configuration.
You can check the typical runway configurations for any major airport in the US on the FAA's OIS webpage.  (http://www.fly.faa.gov/ois/).  On the left side of the page, click on East Directory or West Directory.  Expand the directory tree under the ARTCC (ZDV for Denver, for example) desired and then click on the airport.  The resulting table will show you typical configurations and the number of aircraft arrivals per hour that can be accommodated under each configuration.

This is incorrect. Runway 16R is routinely used for arrivals.


text:
Why should AKE LD3s not be used in the A380?
I noticed some LD3 ULDs (Unit load device, container type LD3) - like AKE (LD3 without forklift holes/half ALF) - mention DO NOT USE A380. What is the difference between normal LD3 and A380 LD3?

AKE seems to be compatible with A380, according to this.

Where are you seeing DO NOT USE WITH A380? Do you see it painted on the containers? Everywhere I look shows them being compatible

I have seen emirates containers.

DO NOT USE ON A380. This comment is mentioned on LD3 AKE.

Emirates uses multiple kinds of ULDs.
The AKE with "DO NOT USE WITH A380" are made out of aluminum metal. The tare weight is 80 kg. Contrasted with the AKE (light weight) 66 kg tare weight and the AKL (ultra light weight) 56 kg tare weight, the difference may seem small, but multiplied over the large number of AKEs can reduce the payload and therefore fuel burn considerably.
Emirates Skycargo website.


text:
How fast can fuel be siphoned out if you leave the cap off?
It is a dreaded scenario; forgetting to secure the fuel cap.
I understand the low pressure area generated above the wing will siphon fuel out of wing tanks, how fast would this happen in a smaller GA airplane with wing tanks (something like the Cherokee perhaps) if the fuel cap was to be completely forgotten (rather than just not tightened)? Also, would it be able to suck the tank completely dry or would there be some limit to the amount of fuel that might be lost this way?
I just had X-plane do this to me while doing some IFR practice and it reduced my fuel with about 2 gallons/minute per tank until they were both completely empty and I was wondering if this is realistic.

In this situation, the tanks were completely empty resulting in a crash.

Digression but it might amuse, quoting an old song collected by Oscar Brand: "He filed her up with high octane / He left the gas cap off again / I'm flying now on dirt and rain / All honor to the Line Boy!"

It can happen very quickly.
I don't have exact numbers, but an acquaintance had this happen in a Cessna 172 and the entire tank was emptied in just a few minutes - the amount of time it took to do one circuit of the pattern and land. The fuel cap was not in the filler neck on departure, and was hanging from the chain, banging against the wing. The moral of that story is: never assume the fuelers put the cap back in.

I've personally flown an older Cherokee 160 that had a loose fuel tank gasket. When doing slow flight, the pressure above the wing was so strong that it would start to ooze fuel from the cap. Fuel would flow in a rather frightening amount back along the wing, and that's with the cap still on.

The specific rate of fuel loss would vary based on a number of factors (angle of attack & speed being the big ones) - The 2gal/minute number above sounds reasonable for a missing cap in cruise.

Don't aircraft have some reserve fuel tank, separate from the primary tank, in case something like this happens

@Firee That sounds like a potential new question :)

As much as I don't like climbing up to the wing, I always dip the tanks after the filler's done to see for myself how much fuel I actually have before taking off. Obviously I'd detect an open fuel cap at this point. That might be a little paranoid, but I think it's better than unscheduled glider practice.

I was once passenger/safety-pilot in a Cessna 150 where the gasket between the tank and the wing skin had failed. Looked over my shoulder before the first turn onto crosswind and discovered that the rear windshield was utterly covered in fuel - easily a couple of litres a minute. And that was with the cap firmly in place (the first thing we checked after shutdown!).
It was a long time ago, but I think the engineers said it had been sucked out through the flap tracks and we probably had a wingful of fuel vapour. Nice...

I've actually had this happen to me too. It started spewing out fuel if I did an aggressive slip towards the wing with the faulty seal, not while coordinated though (slow or otherwise). It was a low wing aircraft, with the caps in plain view, so at least I knew it had stopped so I didn't declare an emergency (and I knew I had enough fuel in the other tank). Needless to say, I rather abruptly turned towards the closest airport for a precautionary landing.

A friend of mine once flew about 2.5 hours with a friend in a 1975 172M after topping-off and forgetting to cap one of the tanks. The flight included some IFR practice maneuvers- turns, constant-speed climbs and descents, etc.
Upon landing and refueling, he discovered, in horror, the uncapped tank. He was surprised to find that he only needed to add about one gallon more than his expected fuel burn should have used up, so if it was siphoning out, it was only a trickle.
The chained cap must have been banging against the wing, though, because it left some marks.
Fuel starvation is obviously a critical situation, and I'm sure it's not the same in all aircraft, but the 172 did okay with one missing cap.


text:
Is flying at 14,000 MSL safe for children without supplemental oxygen?
FAR 91.211(a) requires supplemental oxygen for all passengers above 15,000 feet.  Are there any health implications of a 5 hour flight at around 14,000 feet on children without any supplemental oxygen?  Obviously the flight crew would be wearing supplemental oxygen as required by the FAA above 12,500 feet.
I've read that babies under 3 months do not have mature enough lungs for altitude stress, so for the sake of this question, let's assume the children are over 6 months with no existing health conditions to worry about.
My question is for a non-pressurized general aviation aircraft.

This is not the right place to ask.  You should seek professional medical advice.  Personally, I wouldn't even think about this with kids under about 4-5 years of age.

Even if a doctor says it is ok I would be bringing O2 with a mask for children.  Better to carry those extra 20 pounds just in case.

Let me start out by saying that Aviation Stack Exchange is not a substitute for medical advice. Most of us aren't doctors (though I have medical training I am certainly not a doctor), and even if we were doctors we are not your doctor and we don't know your medical history (or your child's medical history).
If you're going to be flying with your kids in an unpressurized aircraft consult your pediatrician for their recommendation on supplemental oxygen. There are a number of factors at play, and your doctor will be able to consider all of them and give you comprehensive advice.

That said, let's talk about oxygen in general terms.
There's a lot of good information on supplemental oxygen use out there: AOPA talks about it here, and this website has a very detailed explanation, written by a doctor which get into what's going on as altitude increases (and the partial pressure of oxygen in your lungs decreases).
By regulation you are required to provide supplemental oxygen:

to the flight crew if you're above 12,500 feet for more than 30 minutes.
to the flight crew if you're above 14,000 feet for ANY length of time.
to everyone onboard if you're above 15,000 feet for ANY length of time.

Using the handy chart in the second website that equates to oxygen saturations (SpO2) of roughly 88%, 82%, and 76%, assuming you're breathing ambient air for an extended period of time.
To put this into perspective if you come to the hospital with an oxygen saturation below 90% you will almost universally be put on supplemental oxygen, and most guidelines call for maintaining SpO2 above 92%. (In aviation terms, the partial pressure of oxygen at 10,000 feet usually results in SpO2 around 90%).
So with that information the question now becomes "What is your standard of care for your passengers?" - the FAA sets minimum requirements in the regulations, and they are mainly focused on making sure the flight crew does not become impaired (they are less concerned about your passengers getting loopy, as long as the pilot is OK), but you as a pilot are free to set higher standards based on your own understanding of physiology and aeromedical factors.
I can't tell you what you should do, but I can tell you what I do: On any flight above 10,000 feet I carry supplemental oxygen, I use it, and I provide it to my passengers.
I also carry a pulse oximeter in the aircraft to check oxygen saturation (SpO2) on myself or my passengers as needed (and I set the oxygen flow rate based on having the worst person in the aircraft above 90%).

There are always health implications at higher altitudes, even those approved by the FAA.
Legally you are not prevented from flying at this altitude since the FAA does not stipulate an age for that particular FAR. You SHOULD consult a pediatrician on the specifics of you trip and its effects on children of the age you intend to carry. A 3 month old baby and a 4 year old kid are two very different things. If you have not seen it this AOPA article covers everything nicely. It should also be noted that breathing pure O₂ can also be harmfull when its not needed. You SHOULD NOT assume that a solution to the problem is to provide supplemental 02 to children to counter what ever different effects they see due to their differing bodies.
If you do intend on this you should read up on the signs of hypoxia in both adults and children. You should also carry an O₂ meter (possibly one for every occupant (Im not sure what the regs are on that)). I would also consider carrying something like this as a back up source of O₂. The most important thing that you need to plan for is the ability to divert (or descend substantially) in route should you begin to see signs of hypoxia.
DISCOLURE: I am not a doctor (or medical professional of any kind) and this information should be used a guidance and not taken as hard and fast fact. You should always consult a medical professional in cases like this.

The regs (at least FAA regs) say nothing about carrying pulse oximeters. As far as they're concerned it's fancy baggage. Carrying at least one onboard in an unpressurized aircraft is probably a good idea though.

If a pulse oximeter is a good idea for the adults, he should get one for the baby. Babies get their own pulse oximeter attachment due to their size.


text:
How to Recover from a Spin in Cessna 172?
How to recover from a spin in a Cessna 172 ? What are the different maneuvers that a pilot would have to use to to do so?

Isn't it described in the operating handbook? Nevertheless, in the aircraft I've received instruction: C-152, Piper Cherokee, Piper Tomahawk, all the same: (1) full opposite rudder until rotation stops, (2) lower nose to regain airspeed, (3) recover from dive and apply power.

The C172 recovers very easily from spins - in fact you usually have to force it to enter one and then hold it there - so this question might also be interesting

In a 172 just let go of the controls, it'll fly itself out. Just recover from the steep spiral without over-g or over speeding.

Some of the above answers-in-comments show why it's a good idea to go to the POH for an answer.

A few of these coments omits (forgets?) the most important part of PARE, power off!  IRL the same applies, it is not uncommon to forget pulling power to idle.

The memory aid is PARE:

POWER to idle
AILERONS neutral
RUDDER on the floor opposite the direction of spin
ELEVATOR nose-down to break the stall

You will want to read the full explanation in the Pilots Operating Handbook or POH for an understanding of the steps and why you need to take them. Commit the sequence above to memory and better yet get spin training from a qualified instructor.
The POH for the 172N model reads (caps and boldface in original):

Should an inadvertent spin occur, the following recovery procedure should be used:

RETARD THROTTLE TO IDLE POSITION.
PLACE AILERONS IN NEUTRAL POSITION.
APPLY AND HOLD FULL RUDDER OPPOSITE TO THE DIRECTION OF ROTATION.
JUST AFTER THE RUDDER REACHES THE STOP, MOVE THE CONTROL WHEEL BRISKLY FORWARD FAR ENOUGH TO BREAK THE STALL. Full down elevator may be required at aft center of gravity loadings to assure optimum recoveries.
HOLD THESE CONTROL INPUTS UNTIL ROTATION STOPS. Premature relaxation of the control inputs may extend the recovery.
AS ROTATION STOPS, NEUTRALIZE RUDDER, AND MAKE A SMOOTH RECOVERY FROM THE RESULTING DIVE.

NOTE
If disorientation precludes a visual determination of the direction of rotation, the symbolic airplane in the turn coordinator may be referred to for this information.

Other Spin Recovery Methods
The methods below may or may not recover from all spins. Seek out a qualified instructor for spin training — or, better yet, avoid spins altogether!
Finagin

Finagin advocates a four-step recovery technique for unintentional spins and departures from controlled flight that pilots can put to use without hesitation — and without fear of making the situation worse — even when they’re confused or disoriented by the unusual attitudes and strange sensations that can accompany spins.

Rip the power to idle.
Forcefully neutralize the stick and rudder pedals.
Look at the airspeed indicator, and once it shows 100 knots or more (roughly 1.4 times the airplane’s stall speed) …
Pull out of the dive.

Source: AOPA
Beggs-Mueller

Power – Off.
Remove your hand from the stick.
Apply full opposite rudder until rotation stops.
Neutralize rudder and recover to level flight.

Source: Spins in the Pitts Special by Gene Beggs
Hands In Your Lap
Some advocate the “hands in your lap” method of pulling power, taking your hands (and feet) off the flight controls, and waiting for the airplane to fly itself out of the spin. This may work for certain airframes but not all. Catherine Cavagnaro of Ace Aerobatic School says she likes to perform spin training in a Cessna 152 because that airplane will not self-recover from a spin.

That's the NASA answer. It works in many but not all airplanes. In particular, some airplanes need a very swift push forward on the stick to break the stall while in the spin. Neutral elevator won't do it.

I don't know if its just me... but I've found the many "memory aids" in aviation to be more difficult than just rote memorization... when trying to recall,  is it PAIR? or PARE?  What exactly is TOMATO FLAMES?  A FAST MOOSE? APES? RAW FAT?  These aren't helping me. :)

A key point here is If disorientation precludes a visual determination of the direction of rotation, the symbolic airplane in the turn coordinator may be referred to for this information. I've heard if you haven't been in a spin before (or very often) it is hard to tell what direction you are actually spinning, so looking at the turn coordinator can help you figure that out.

Once I found myself in that situation, and got so scared, that I forgot which pedal should be pushed... Fortunately, I had enough altitude, kept pushing the stick, and the plane flew out of the spin by itself...

I always taught my students the acronym PARE:
P: Power idle. This reduces the airflow over the tail. This may seem counterintuitive, but it's about helping to lower the nose and break the stall. The less airflow over the tail, the lower its downward lift component will be. This will in turn allow the aircraft's nose to drop, helping to break the stall.
A: Ailerons neutral. This may also seem counterintuitive, as your natural urge will be to put opposite aileron in to level the wings. But in a stall, one wing is more stalled (higher angle of attack) than the other. Let's say it's the left wing. If you were to add right aileron to bring that left wing back up, that means that the left wing's aileron will go down in an attempt to create more lift on that wing. But by lowering the aileron on that wing you will actually be increasing the angle of attack on that wing, which in turn will only deepen the stall on the wing and worsen the spin.
R: Rudder full opposite the spin. This is the key step, and in most Cessnas will be enough on its own to dampen or end the spin pretty fast. It counteracts the yaw and roll of the spin.
E: Elevator nose down to break the stall (after applying the opposite rudder). This will be like an exaggerated stall recovery, as you will likely have a very nose low attitude. However, this step is key on some aircraft to break the stall.
All aircraft have different stall and spin characteristics. Some are certified for spins, some aren't but will recover easily, and some will not recover well at all. Consult your aircraft's POH to learn about your aircraft's characteristics and certifications, and don't attempt to learn by yourself; always fly with an instructor if you intend to practice spin recoveries.

First lesson from my CFI to recover from a spin:  Feet on floor, hands in your thighs.  This is called the Beggs/Mueller recovery technique.
The 172 is a "stable" plane.  So, as i understand it, if it were dropped from upside down or on its side from a cargo plane, it will right itself.

Well, this goes against what the Pilot's Operating Handbook says. I'm not saying that a Cessna 172 won't recover from a spin if you just take your hands and feet off the controls, but I'm wary of any advice that contradicts the POH.

From someone who has done it in a 172, this is a stable plane.  If you stall, just let go of the yoke but KEEP THE NOSE STRAIGHT WITH THE RUDDER PETALS.  You still have control of your rudder, work those petals.  The nose will gently drop (with maybe a little shudder), nose down with elevator and recover,  Do not apply ailerons until you are flying.  You can work on power on and power off stalls with your instructor.  Use PARE.

I wonder if what was stated in this answer really works for all allowable CG positions for this aircraft.  Two people in front may be a world of difference than lots of weight in back too.  I would trust the POH advice more than this recommendation.

Hi Bill, welcome!  I've added a link to the technique to your post.


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Is it possible to "take a bullet [missile]" for another plane as shown in the movie Air Force One?
In Air Force One a fighter jet maneuvers between a missile and the president's plane, as shown in this clip.
Is such a maneuver possible?
If not, what could be done in that situation?

It's difficult to count how many moments of BS there are in that clip - but that's Hollywood.  It wouldn't be half as much fun if it was realistic.

Possible and Plausible are two different things.

Is it possible to fly a fighter jet between a missile and another aircraft, and either (a) confuse that missile so it follows the fighter instead) or (b) have the fighter be hit by the missile instead of the original target aircraft? Yes.
Modern fighters are capable of maneuvering in the manner shown: they can even sustain knife-edge flight or vertical climb for a while. It's even possible that in a moment of desperation a pilot would attempt such a maneuver, sacrificing themselves and their aircraft to save their commander-in-chief.
(The G-forces involved in these maneuvers may be unpleasant or even unbearable for the pilot, but if you're committing yourself to a course of action that ends with your plane blowing up to save another plane the G-forces are probably the least of your concerns.)

It isn't plausible that such a maneuver would work - at least not as depicted in the movie.
Missiles are REALLY FAST - this footage includes several slow motion shots of an air-to-air missile as it's fired (at it's slowest relative velocity), and it's still pretty darn quick: It's gone in a few frames of high-speed footage.
For this maneuver to work the intercepting pilot would need to be in exactly the right position and exactly the right time, and perform the maneuver perfectly in order to intercept the missile: A little error in any direction - too fast, too slow, too far left, or too far right - and the  missile would fly right past them and continue on toward its target.
The intercept is further complicated by the fact that, assuming the missile is guided, both the missile and the target are maneuvering as well.
(If it's a non-guided "dumb" missile all the target aircraft needs to do is change course to avoid being hit - a maneuver that might stress the airframe a bit, but certainly less than being hit by a missile would.)

To give a little more context, the "anti-missile missile" programs have often been described as having your friend throw a baseball over the roof of your house while you stand on the other side and try to hit it with a golfball as it comes over the top.
This intercept is of similar difficulty, except the balls involved are all steering themselves toward different objectives.

How accurate is that description/analogy?  One obvious difference between a missile and a golf ball is that a golf ball doesn't have a blast radius.  This means that the accuracy requirement is significantly easier, as you don't actually need to physically strike the missile you're trying to intercept; you just need to get close enough to it.

@MasonWheeler For the anti-missile missiles The blast radius is why it's a golf ball and not a pea - you still need to be pretty "close" in order for the explosion to definitely take out the other missile (if you have a larger explosive yield on the interceptor you might be throwing a basketball). The fighter of course doesn't have a blast radius unless it gets hit (though it's somewhat larger than an interceptor missile, so I'd call that a wash).

I'm pretty sure the only way to make the timing precise enough to get the fighter in the right place at the right time so it could intercept the missile would be if the pilot turned over control to the R2 unit in the back. Oh oops, wrong movie, though just as realistic.

@MasonWheeler most (modern) anti-ballistic missiles are kinetic kill systems - they don't have a blast radius. Older missiles did use warheads, some nuclear.

Spacecraft docking in orbit has also been described as "person A standing on one side of a house, person B standing on the other side of the house, person A throws a tennis ball over the roof, person B tries to throw a rock to hit it as it comes sailing over". Thankfully in the case of spacecraft orbital maneuvering, the spacecraft are typically friendly to each other, at least one is in a relatively well-known orbit, and the other is in an original orbit planned for the rendezvous.

@Johnny Don't underestimate the Force. https://www.youtube.com/watch?v=L4EdtpCvF8I

A good pitcher could probably actually pull off the ball trick, so that might not be the best analogy.


text:
How does a CFI know what endorsements to give?
I am trying to figure out how a CFI knows what endorsements to give. Obviously AC 61-65E lays them out but what if someone is coming from a unique situation? Let's say someone has a helicopter license and wants to get their private pilot? Do they have to take a knowledge test? What if someone is a sports pilot and wants to upgrade to a private pilot, what do they have to do? How do you figure it out?

. . . is there really a situation not covered by AC 61-65? It's pretty thoroughly cross-referenced into the FARs. There are other things that need to be logged (e.g. you need log entries showing dual instruction and/or solo time meeting whatever aeronautical experience requirements are applicable for a given certificate or rating), but those aren't "endorsements" - they're just logbook entries (albeit with a CFI's signature when instruction was given to certify that they did in fact give such instruction).

Lets cover your specific questions first.

Let's say someone has a helicopter license and wants to get their
  private pilot? Do they have to take a knowledge test?

(it appears I was initially incorrect and the knowledge test does not need to be repeated as per RDP's answer  below)
According to FAR 61.63 you don't need to retake the knowledge test

(b) Additional aircraft category rating. A person who applies to add a
  category rating to a pilot certificate:

(1) Must complete the training
  and have the applicable aeronautical experience.
(2) Must have a
  logbook or training record endorsement from an authorized instructor
  attesting that the person was found competent in the appropriate
  aeronautical knowledge areas and proficient in the appropriate areas
  of operation.
(3) Must pass the practical test.
(4) Need not take an
  additional knowledge test, provided the applicant holds an airplane,
  rotorcraft, powered-lift, weight-shift-control aircraft, powered
  parachute, or airship rating at that pilot certificate level.

The FAR's pretty much cover all the the various cases however they can be a bit confusing.

What if someone is a sports pilot and wants to upgrade to a private
  pilot, what do they have to do? How do you figure it out?

In terms of endorsements you must obtain an endorsement for what ever it is you are going to do (exam, practical test, etc.) even if you have a license in another class or category. For example if you are going to take the PPL check ride you need an endorsement for that check ride (even if you have a sport pilots license). Now when it comes to training things may differ. Your training for a PPL will obviously be shorter if you have a sport pilots license but you will still be required to take the Private Pilots Single Engine Land written test and practical test and receive endorsements to do so, to get a PPL. This site covers the transition from Sport Pilot to Private Pilot nicely. If you are transitioning from sport to private I would imagine you may be able to complete all the requirements for a PPL without having received the student solo endorsement since you could in theory have accomplished all your solo flight requirements as a sport pilot.
Personal Note: Its always a good idea to speak with your DPE before taking any practical test and ask what endorsements he is expecting to see in your log book (which should be the ones that are required and no more (or less for that matter)). When I went for my check ride the wording for the PPL practical endorsement had changed recently and he warned me that many instructors mess up the wording or the pre printed ones in the log book are out of date and it can be an issue. I had my instructor add the necessary line before I went for my check ride.

This answer is demonstrably wrong.

Rounding Pi to 3.2 is valid for some engineering calculations and i have edited my answer to reflect your correction. However for the record I copied the FAA's text and took nothing from your answer.

yes, rounding to 3.2 is acceptable. changing an answer from no to yes is not.

How is that not acceptable, there was an error in my response which i corrected and have not cited your answer within mine as the source of the correction. For what its worth I changed my answer for yes to no.

In general, a flight instructor must demonstrate sufficient knowledge so as to be able to provide the proper endorsements for his students. This is covered both in AC 61-65 and in the Flight Instructor Practical Test Standards Task M:

Task M: Logbook Entries and Certificate Endorsements
References: 14 CFR part 61, AC 61-65.
Objective: To determine that the applicant exhibits instructional
  knowledge of the elements related to logbook entries
  and certificate endorsements by describing:

Required logbook entries for instruction given.
Required student pilot certificate endorsements, including
  appropriate logbook entries.
Preparation of a recommendation for a pilot practical test,
  including appropriate logbook entry for:
  a. Initial pilot certification.
  b. Additional pilot certification.
  c. Additional aircraft qualification.
Required endorsement of a pilot logbook for the satisfactory
  completion of the required FAA flight review.
Required flight instructor records.

Regarding the question:

Let's say someone has a helicopter license and wants to get their private pilot? Do they have to take a knowledge test?

According to 61.63:

§ 61.63 Additional aircraft ratings (other than for ratings at the airline transport pilot certification level).
(b) Additional aircraft category rating. A person who applies to add a category rating to a pilot certificate:
(4) Need not take an additional knowledge test, provided the applicant holds an airplane, rotorcraft, powered-lift, weight-shift-control aircraft, powered parachute, or airship rating at that pilot certificate level.

So a private pilot looking to add an additional category rating at the same certificate level need not take the aeronautical test.
Regarding the question:

What if someone is a sports pilot and wants to upgrade to a private pilot, what do they have to do?

you can find the answer in part 61.103:

Subpart E—Private Pilots
§61.103   Eligibility requirements: General.
To be eligible for a private pilot certificate, a person must:
(e) Pass the required knowledge test on the aeronautical knowledge areas listed in §61.105(b) of this part.
(j) Hold a U.S. student pilot certificate, sport pilot certificate, or recreational pilot certificate.

So a sport pilot upgrading his certificate to private pilot must take the private pilot test.

These are good questions - I usually google the situation or search the FARs, or lastly make a phone call to your local FSDO. Each of those situations is unique / different, and sometimes even the FSDO has to do some research.


text:
Can I file a VFR flight plan for a training flight?
Let's say you are going to do some maneuvers in a practice area, make a few touch and go landings at a non-towered airport, then return to your home airport...is it possible to file a VFR flight plan for this?

I don't see any reason why you could not, especially if the practice area or T&G airport is far enough away from the airport. I can't say I've ever done a VFR flight plan for practice area/T&G's unless it were cross-country though. If you need practice with VFR flight plans I'd say go for it. I always find it funny that news of crashes for training flights always says "no flight plan was filed"... like most people file flight plans for pattern work...

Are you talking about filing VFR flight plans in the US (FAA flight plans), or elsewhere?

@voretaq7 US (FAA)

Absolutely. In fact it's not a bad idea to do so, if only to get some practice filing flight plans and using the system.
In the US VFR flight plans are a search-and-rescue tool: They're only used if your aircraft is overdue to give the rescue folks information to help plan the search.
In your particular case I would file a flight plan that lists your home airport as your departure and destination, with the airport you intend to use for your touch-and-go landings as an intermediate waypoint.  If you want to enter information on the nature of the flight (training, touch-and-gos at XXXX, etc.) in the remarks field you can do that too.
Activate the flight plan when you depart, and close it when you return to your home airport. You can optionally also call Flight Service over the radio when you get to the touch-and-go airport to give them a position report and let them know you've reached that waypoint (I would do this on your way out of the area to return home, along with an ETA update if appropriate).

As an alternative (or in addition to the VFR flight plan) you could get flight following from the ATC facility responsible for your airspace. Be aware that they may drop you and ask you to squawk VFR while you shoot your touch-and-gos since you'll probably be going off their radar, but you can always request service again when you start your return leg.


text:
Does holding a medical certificate mean you automatically have a student pilot certificate?
If you have a 1st, 2nd, or 3rd class medical certificate and a private balloon certificate (as an example) does that mean you have a student pilot certificate if you now want to get a private pilot certificate? Would you have to go back to a medical examiner, DPE, or FSDO to get a student pilot certificate?

Which country are you talking about? Rules vary around the world.

Since you're talking about DPEs and FSDOs I think we can safely assume you're asking about [tag:faa-regulations]?

This answer reflects rulemaking effective 1 April 2016
Regarding the question in the title, no, holding a medical does not mean you have a student pilot certificate.  New regulations going into effect 1 April 2016 separate the student pilot certificate from the combination medical+student pilot certificate.  Students will need to apply for a student pilot certificate with their CFI or with the FSDO (or their part 141 flight school) through IACRA.  The new student pilot certificate is plastic just like a normal pilot certificate and do not expire.
This part is true with or without the rulemaking changes
Regarding the question in the body of your post, you are already a certificated pilot with a balloon rating.  You are not a student pilot, you are a private pilot.  The regulations you are subject to are to add an airplane category rating are in 14 CFR 61.63.

§61.63   Additional aircraft ratings (other than for ratings at the airline transport pilot certification level).
(a) General. For an additional aircraft rating on a pilot certificate, other than for an airline transport pilot certificate, a person must meet the requirements of this section appropriate to the additional aircraft rating sought.
(b) Additional aircraft category rating. A person who applies to add a category rating to a pilot certificate:
(1) Must complete the training and have the applicable aeronautical experience.
(2) Must have a logbook or training record endorsement from an authorized instructor attesting that the person was found competent in the appropriate aeronautical knowledge areas and proficient in the appropriate areas of operation.
(3) Must pass the practical test.
(4) Need not take an additional knowledge test, provided the applicant holds an airplane, rotorcraft, powered-lift, weight-shift-control aircraft, powered parachute, or airship rating at that pilot certificate level.

As a balloon pilot seeking the airplane category rating with the single-engine land class you

must meet the aeronautical experience requirements in 61.109(a)
must be endorsed and found competent in aeronautical knowledge of 61.105(b), 61.107(b)(1)
must complete a private pilot airplane written exam

and then you will be able to take the practical examination and have airplane single-engine land added to your existing private pilot certificate.

What about an additional category rating from 61.63(b)?

@jskypilot I'm not sure what you are asking. My answer already addresses 61.63(b).

Would this endorsement be necessary?  68. Additional aircraft category or class rating (other than airline transport pilot (ATP)):
§§ 61.63(b) or 61.63(c).
I certify that (First name, MI, Last name), (pilot certificate), (certificate number), has received
the required training for an additional (name the aircraft category/class rating). I have determined
that he/she is prepared for the (name the practical test) for the addition of a (name the aircraft
category/class rating).
/s/ [date] J. J. Jones 98

So to summarize 4 endorsements: knowledge test endorsement (61.35), flight proficiency and aeronautical experience endorsement (61.107, 61.109), received training in last two months, covered knowledge test deficiencies, and is ready for practical (61.39), and different category endorsement (61.63). Is all that correct?

@jskypilot yes, you would need all that.  Furthermore for the checkride see the private pilot PTS and see what you'll have to demonstrate for the add-on category/class.  I'm not sure what the balloon rating will give you there, but its likely you won't have to demonstrate everything that a student pilot seeking a private airplane would have to.

Although the other answer is correct regarding the medical, the thing you need to know is that if you already hold a private balloon certificate, you do not need a student pilot certificate.
You are already a private pilot, with a balloon rating, and you are adding an airplane rating.


text:
Is there any use for variable shape wings within aviation?
I am working on a variable shape airfoil which is originally intended for sailboats. However, I am wondering if there might be an application for such a design within aviation? The design I am working on can change thickness, camber, and twist quickly at the same time. The whole wing asymmetry can be mirrored within a second as well.
Is there an application for variable wing shape or geometry similar to this in aviation?

You may like to look into wing warping, used for old aircraft designs in the early 1900s (before hinged control surfaces became the universal standard). It may be possible if you can deal with the mechanical challenges. Also you should put a little more information on your question, as the website link looked like spam (someone has already removed it.)

The F-14 Tomcat (and others) have a simple form of variable wing geometry (variable wing sweep)

There are swing-wings, pivot wings and variable AoA wings, so I'd say "Yes".

Wing re-shaping or flexing is not an outdated technology. Several modern efforts are exploring such applications using new material technologies. There is definitely an application for such designs within aviation, especially when used as in ways to replace control surface or flap designs.

Well I guess Krueger flaps are a form or variable shape wings. I can't see why other means cant be of use. https://en.wikipedia.org/wiki/Krueger_flap

Well, yes.
Variable shape wings (or variable geometry) have a number of uses, primarily in being able to optimize the shape of the wing to an ideal form for the regime of flight.
The idea isn't new; birds, bats and other flying creatures twist and warp the shape of their wings in order to maneuver and generate thrust as these pigeons demonstrate.

The Wright Brothers used a warping wing box on their gliders and the 1903 flyer.  Orville Wright is said to have come up with the idea while twisting a rectangular cardboard box used to ship bicycle tire inner tubes.

The chief advantages to such a design are that it provides an extremely clean airframe, aerodynamic wise, without joints, separate control surfaces, moving parts, etc which create excess drag.  In addition, the aircraft shape can automatically be optimized to the altitudes, speeds and Mach numbers desired without tradeoffs for weight or performance required with aircraft made from conventional materials.
The downside to warping wings is solving the problem of finding materials which could be flexible and change their shape and then remain rigid and immutable under aerodynamic loads.  Wood and metal airframes lacked the capability to do this successfully.
Early attempts to solve this problem have been to make 'swing wing' designs where the wing can be rotated at the wing root to an  optimal sweep in flight.  The Bell X-5 successfully demonstrated this concept and it has been used on a number of military aircraft including the F-111, F-14, MiG-23/27, B-1, and SU-22.
NASA is currently developing a morphing wing for these reasons.  If successful and shown to be feasible from a manufacturing and service standpoint, it would be a game changer.